Labile carbon and nitrogen dynamic change in soils incorporated with different parts of maize plants

An incubation experiment was carried out to investigate the labile carbon and nitrogen dynamic changes in soils added with different parts of maize plants (straw, root, stem and leaf). The strawamended soils had been incorporated with both straw and root residues, and the control soils with only root residues in consecutive sevenseasons of summer maize and winter wheat rotation system in Guanzhong Plain, Shaanxi province, China. The soil microbial biomass carbon (SMBC), soil microbial biomass nitrogen (SMBN), dissolved organic carbon (DOC), mineral nitrogen are determined regularly over 62 days, incubation. The results show that soil labile carbon and nitrogen change rapidly in the first 7 days. The contents of SMBC and SMBN amended with straw are significantly (P0.05) higher than those with root. The SMBC and SMBN contents are greater in soils added with leaves than with stems at the first 28 d and 14 d incubation, and opposite afterwards. The SMBC and SMBN contents in soils added with straws are in between of the leaves and stems additions. The soil DOC and mineral nitrogen contents are in the order: leaf straw stem root. At the end of the incubation, both the SMBC and mineral nitrogen contents increased significantly, soil DOC contents kept unchanged and the SMBN contents declined in all straw parts treatments. Compared to the non-added soils, the straw-added soils had no significant effect on the decomposition of fresh residues, and the differences in soil labile N between the two soils are greater than those in soil labile C. Therefore, soil labile C and N dynamics are influenced primarily by the ratio of C to N in the different straw parts. A same amount of straw is more efficient in replenishing soil C and N than roots after incorporated into soil, and the soil labile N is more sensitive than C to straw addition.